Difference between revisions of "FIND Examples"
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− | ==Introducing the | + | ==Introducing the '''world''' collection of countries== |
− | + | <p>These examples introduce NoSQL using MongoDB. We will be using the <syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> command on the '''world''' collection .</p> | |
− | + | <div class="q" data-lang="mongo"> | |
− | + | By default, <syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> returns the entire contents of a collection. This is equivalent to <syntaxhighlight lang="JavaScript" inline>find({})</syntaxhighlight> | |
− | + | <p class="strong">Show all the documents in world</p> | |
− | + | <pre class="def"><nowiki>db.world.find();</nowiki></pre> | |
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− | <p class=strong>Show all the documents in world</p> | ||
− | <pre class=def> | ||
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− | </ | ||
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− | </ | ||
</div> | </div> | ||
− | <div class=q data-lang=" | + | ==find and findOne== |
− | It is also possible to just return the first document with | + | <div class="q" data-lang="mongo"> |
− | + | It is also possible to just return the first document with <syntaxhighlight lang="JavaScript" inline>findOne()</syntaxhighlight>. | |
− | + | <p class="strong">Show the first document of world</p> | |
− | </ | + | <pre class="def"><nowiki>db.world.findOne();</nowiki></pre> |
− | <p class=strong>Show the first document of world</p> | ||
− | <pre class=def> | ||
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− | </ | ||
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− | </ | ||
</div> | </div> | ||
− | <div class=q data-lang=" | + | ==skip and limit== |
− | It is also possible to skip | + | <div class="q" data-lang="mongo"> |
− | <p class=strong>Get the 50th document of world</p> | + | It is also possible to retrieve a specific document based on its position using <syntaxhighlight lang="JavaScript" inline>skip(n-1)</syntaxhighlight> and <syntaxhighlight lang="JavaScript" inline>limit(1)</syntaxhighlight>.<br/> |
− | <pre class=def> | + | As this is JavaScript you can also access by index: <syntaxhighlight lang="JavaScript" inline>db.world.find()[n-1];</syntaxhighlight> |
− | + | <p class="strong">Get the 50th document of world</p> | |
− | + | <pre class="def"><nowiki>db.world.find().skip(49).limit(1);</nowiki></pre> | |
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− | </ | ||
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− | </ | ||
</div> | </div> | ||
==Querying== | ==Querying== | ||
− | <div class=q data-lang=" | + | <div class="q" data-lang="mongo"> |
− | + | <syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> can filter results if a document is used as an argument. | |
− | <p class=strong>Get all the data concerning france</p> | + | <p class="strong">Get all the data concerning france</p> |
− | <pre class=def> | + | <pre class="def"><nowiki>db.world.findOne({name: "France"});</nowiki></pre> |
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− | </ | ||
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− | </ | ||
</div> | </div> | ||
− | <div class=q data-lang=" | + | ==Using a projection with find== |
− | By passing a second parameter to find() the output can be limited to certain field(s)<br/> | + | <div class="q" data-lang="mongo"> |
− | In this example 1 indicates "true | + | By passing a second parameter to <syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> the output can be limited to certain field(s)<br/> |
− | A feature of MongoDB is the [http://docs.mongodb.org/manual/reference/object-id/ ObjectID] or | + | In this example '''1''' indicates <syntaxhighlight lang="JavaScript" inline>true</syntaxhighlight> and '''0''' indicates <syntaxhighlight lang="JavaScript" inline>false</syntaxhighlight><br/><br/> |
+ | A feature of MongoDB is the [http://docs.mongodb.org/manual/reference/object-id/ ObjectID] or '''_id'''.<br/> | ||
This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be <b>explicitly</b> set to false to be excluded from the results set.<br/> | This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be <b>explicitly</b> set to false to be excluded from the results set.<br/> | ||
− | <p class=strong>Get the population of Germany</p> | + | <p class="strong">Get the population of Germany</p> |
− | <pre class=def> | + | <pre class="def"><nowiki>db.world.findOne({name: "Germany"}, {population: 1, _id: 0});</nowiki></pre> |
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− | </ | ||
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− | </ | ||
</div> | </div> | ||
− | <div class=q data-lang=" | + | ==Comparisons== |
+ | <div class="q" data-lang="mongo"> | ||
MongoDB also allows comparisons. Syntax: | MongoDB also allows comparisons. Syntax: | ||
<pre> | <pre> | ||
+ | <nowiki> | ||
Mongo | MySQL | Mongo | MySQL | ||
-------------- | -------------- | ||
Line 92: | Line 54: | ||
$in | IN | $in | IN | ||
$nin | NOT IN | $nin | NOT IN | ||
+ | </nowiki> | ||
</pre> | </pre> | ||
− | <p class=strong>List the countries with a population that's less than 1 million.</p> | + | <p class="strong">List the countries with a population that's less than 1 million.</p> |
− | <pre class=def> | + | <pre class="def"><nowiki>db.world.find({population: {$lt: 1000000}}, {name: 1, _id: 0});</nowiki></pre> |
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− | </ | ||
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− | </ | ||
</div> | </div> | ||
− | <div class=q data-lang=" | + | ==Logical operations $and $or $not== |
− | It's also possible to have multiple conditions for an $and, $or, etc. This can be done in several ways, for example: | + | <div class="q" data-lang="mongo"> |
− | < | + | It's also possible to have multiple conditions for use in an '''$and''', '''$or''', etc. This can be done in several ways, for example: |
− | db.<collection>.find({<first condition>,<second condition>} | + | <syntaxhighlight lang="JavaScript"> |
− | db.world.find({ | + | // AND (implicit) |
+ | db.<collection>.find({<first condition>, <second condition>}); | ||
+ | db.world.find({population: {$lt: 1000000}, area: {$gt: 200000}}); | ||
+ | |||
+ | // AND (explicit) | ||
+ | db.<collection>.find({$and: [<first condition>, <second condition>]}); | ||
+ | db.world.find({$and: [{population: {$lt: 1000000}}, {area: {$gt: 200000}}]}); | ||
+ | |||
+ | // OR | ||
+ | db.<collection>.find({$or: [<first condition>, <second condition>]}); | ||
+ | db.world.find({$or: [{population: {$lt: 1000000}}, {area: {$gt: 200000}}]}); | ||
+ | </syntaxhighlight> | ||
− | + | <p class="strong">Find the countries with less than 1 million people, but over 200000km<sup>2</sup> area.</p> | |
− | + | <pre class="def"><nowiki>db.world.find({population: {$lt: 1000000}, area: {$gt: 200000}}, {name: 1, _id: 0});</nowiki></pre> | |
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− | <p class=strong>Find the | ||
− | <pre class=def> | ||
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− | </ | ||
− | < | ||
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</div> | </div> | ||
+ | |||
+ | ==$in and $nin== | ||
+ | <div class="q" data-lang="mongo"> | ||
+ | Lists can be used with '''$in''' and '''$nin''': | ||
+ | <p class="strong">Find the continent of Brazil, the United Kingdom, and Ghana.</p> | ||
+ | <pre class="def"><nowiki> | ||
+ | db.world.find( | ||
+ | {name: {$in: ['Brazil', 'Ghana', 'United Kingdom']}}, | ||
+ | {name: 1, continent: 1, _id: 0} | ||
+ | );</nowiki></pre> | ||
</div> | </div> | ||
− | <div class=q data-lang=" | + | ==Regular Expressions== |
− | + | <div class="q" data-lang="mongo"> | |
− | <p class=strong> | + | Pattern matching is possible with Regular Expressions (RegEx)<br/> |
− | <pre class=def> | + | <p class="strong">Show each country that begins with G.</p> [[RegEx_Pattern_Matching | RegEx Pattern Matching]] |
− | + | <pre class="def"><nowiki> | |
− | + | db.world.find( | |
− | ) | + | {name: {$regex: /^G/}}, |
− | </ | + | {name: 1, continent: 1, _id: 0} |
− | + | );</nowiki></pre> | |
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− | </ | ||
</div> | </div> |
Latest revision as of 14:12, 17 October 2018
Contents
Introducing the world collection of countries
These examples introduce NoSQL using MongoDB. We will be using the find()
command on the world collection .
By default, find()
returns the entire contents of a collection. This is equivalent to find({})
Show all the documents in world
db.world.find();
find and findOne
It is also possible to just return the first document with findOne()
.
Show the first document of world
db.world.findOne();
skip and limit
It is also possible to retrieve a specific document based on its position using skip(n-1)
and limit(1)
.
As this is JavaScript you can also access by index: db.world.find()[n-1];
Get the 50th document of world
db.world.find().skip(49).limit(1);
Querying
find()
can filter results if a document is used as an argument.
Get all the data concerning france
db.world.findOne({name: "France"});
Using a projection with find
By passing a second parameter to find()
the output can be limited to certain field(s)
In this example 1 indicates true
and 0 indicates false
A feature of MongoDB is the ObjectID or _id.
This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be explicitly set to false to be excluded from the results set.
Get the population of Germany
db.world.findOne({name: "Germany"}, {population: 1, _id: 0});
Comparisons
MongoDB also allows comparisons. Syntax:
Mongo | MySQL -------------- $eq | == $gt | > $gte | >= $lt | < $lte | <= $ne | !=, <> $in | IN $nin | NOT IN
List the countries with a population that's less than 1 million.
db.world.find({population: {$lt: 1000000}}, {name: 1, _id: 0});
Logical operations $and $or $not
It's also possible to have multiple conditions for use in an $and, $or, etc. This can be done in several ways, for example:
// AND (implicit)
db.<collection>.find({<first condition>, <second condition>});
db.world.find({population: {$lt: 1000000}, area: {$gt: 200000}});
// AND (explicit)
db.<collection>.find({$and: [<first condition>, <second condition>]});
db.world.find({$and: [{population: {$lt: 1000000}}, {area: {$gt: 200000}}]});
// OR
db.<collection>.find({$or: [<first condition>, <second condition>]});
db.world.find({$or: [{population: {$lt: 1000000}}, {area: {$gt: 200000}}]});
Find the countries with less than 1 million people, but over 200000km2 area.
db.world.find({population: {$lt: 1000000}, area: {$gt: 200000}}, {name: 1, _id: 0});
$in and $nin
Lists can be used with $in and $nin:
Find the continent of Brazil, the United Kingdom, and Ghana.
db.world.find( {name: {$in: ['Brazil', 'Ghana', 'United Kingdom']}}, {name: 1, continent: 1, _id: 0} );
Regular Expressions
Pattern matching is possible with Regular Expressions (RegEx)
Show each country that begins with G.
RegEx Pattern Matchingdb.world.find( {name: {$regex: /^G/}}, {name: 1, continent: 1, _id: 0} );